Micropipettors (or syringes) are generally utilized in laboratories and medical facilities for accurately dispensing and/or measuring quantities of liquid. Over the years, many precision micropipettor devices (disposable as well as nondisposable types), capable of precisely dispensing a predetermined amount of liquid easily and rapidly, have been proposed. Many of these pipette devices include spring means surrounding or adjacent the plunger element for accurately assisting an operator's hand motion when an operator depresses the head of the plunger to dispense a predetermined quantity of liquid.
For example, U.S. Pat. Nos. 2,792,157 to Gilman and 2,798,647 to Broadwin, both show liquid dispensing pipettes which are provided with springs which serve to bias the pipette plunger at its uppermost position. Furthermore, U.S. Pat. No. 3,815,790 to Allen et al discloses a liquid dispensing pipette equipped with a spring surrounding the plunger element within the interior of the liquid holding barrel of the pipette. However, these above-mentioned devices are additionally incorporated with spring supporting and gauging structures which made the pipette cumbersome and sometimes difficult to operate under all conditions.
A spring directly between the cap of the plunger and the flange of the barrel of an ordinary syringe is seldom seen because the spring's properties would be destroyed as the syringe expelled about half of its full volume; the spring would be compressed beyond its elastic limit. That is why micropipets do not use ordinary syringes. Micropipets, as seen in the aforementioned patents, have long plunger shafts and correspondingly long springs in order to only slightly reduce the spring length for delivering the full volume of the micropipettor, which is essentially a syringe. Thus, due to the lengths of the plunger elements utilized in these devices, it is necessary to employ long spring devices between the cap of the plunger and the flange of the barrel which often causes the springs to compress beyond their elastic limits destroying the accurate return force of the spring when the pipette is in use; in other words, if the spring is relied upon to return the plunger to its correct starting position, the pipette can only be relied upon to accurately dispense only once. No micropipettor or syringe device has previously been available for allowing an experienced or inexperienced operator to reliably rapidly and easily dispense an accurate amount of liquid repeatedly therefrom.
Additionally, due to the increasingly high cost of medical facility care, self adminstration of medicines by patients at home is becoming a usual practice. As patients depend on accurate amounts of doses, there is a great need for a syringe (or micropipette) which can inject (or dispense) accurate quantities of liquid therefrom repeatedly, rapidly and easily in a reliable way.
Another problem which exists in the prior art is the unavailability of a simple structured, fixed volume, precision micropipettor which is so inexpensive that it can be thrown way after only a few uses without economic disadvantage. At the present time, precision micropipettors are so expensive that throwing them away is not practical; in part this is so because of the presence of additional elements and the design and construction of other elements.